73 Leonis
A binary star system with a K2 III giant primary.
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73 Leonis, also designated n Leonis, is a binary star system located in the constellation Leo. Its combined apparent magnitude of +5.32 makes it just barely visible to the naked eye under optimal viewing conditions. Based on parallax data from the Gaia spacecraft, the system lies about 460 light-years (142 parsecs) away.
The system's binary nature was first proposed in 1920 from spectroscopic observations, and it was confirmed as a binary by two separate studies in 1926 and 1928. The most recent orbital solution, combining spectroscopy, astrometry, and direct interferometric observations, shows the two stars orbit each other every 8.1042 years. Their orbit has an eccentricity of 0.4251 and is inclined at 58.03° to our line of sight.
The angular semi-major axis is 45.470 milliarcseconds, which at the system's distance corresponds to 6.535 astronomical units. Because the orbit is fairly eccentric, the separation between the stars varies from 9.322 AU at their farthest (apoastron) to 3.749 AU at their closest (periastron). The total mass of the pair is 4.24 ± 0.37 solar masses.
The primary star dominates the system's light output. Its spectrum matches a K2 III classification—the "III" indicates it is a giant star that has exhausted the hydrogen fuel in its core. This star has about 26 times the Sun's radius and radiates 195 times the Sun's luminosity from its photosphere, which has an effective temperature of 4,271 K. That temperature gives it the orange color typical of K-type stars.
The secondary star is not well understood. It is 3.62 magnitudes fainter than the primary, and based solely on that brightness difference, it is estimated to have a spectral type of F6V. However, it has never been studied spectroscopically to confirm its spectral type.
Quick Facts
- Constellation
- Leo
- Combined apparent magnitude
- +5.32
- Orbital period
- 8.1042 years
- Eccentricity
- 0.4251
- Inclination
- 58.03°
- Angular semi-major axis
- 45.470 mas
- Semi-major axis
- 6.535 AU
- Separation range
- 3.749 AU (periastron) to 9.322 AU (apoastron)
Facts from the source article.
Background
The binary nature of 73 Leonis was initially suggested in 1920, based on spectroscopic observations. The system was confirmed to be a binary by two studies from 1926 and 1928. The most modern determination of the orbital elements, as of 2025, combines spectroscopy, astrometry, and direct observations from interferometry. It finds that the stars orbit with a period of 8.1042 years, an eccentricity of 0.4251, and an inclination of 58.03°.
The angular semi-major axis is 45.470 mas, which at the distance of 73 Leonis corresponds to 6.535 astronomical units. Given the relatively high eccentricity, the separation between components varies from 9.322 AU at apoastron to 3.749 AU at periastron. The combined mass of the pair is 4.24±0.37 M☉.
The primary star dominates the energy output of the system. Its spectrum matches a spectral class of K2 III, with the luminosity class III indicating it is a giant star that has exhausted the hydrogen at its core. This star has around 26 times the radius of the Sun, radiating 195 times the Sun's luminosity from its photosphere at an effective temperature of 4,271 K, giving it the orange hue typical of a K-type star.
The secondary star is poorly characterized. It is 3.62 magnitudes fainter than the primary, and based on this difference it is estimated to have a spectral type of F6V, although it was never characterized spectroscopically to accurately determine its spectral type.
More in Binary and Multiple Stars
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: 73 Leonis (CC BY-SA 4.0).
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